ABS (antilock brake system) prevents wheels from locking and comes into operation when a higher friction coefficient between a tire and the road is demanded than can be transmitted, i.e. when the driver brakes too hard. In the case of excessively hard braking, the central electronic control unit of the ABS brake system detects the tendency for one or more wheels to lock from rotational speed detector signals and, from these signals, calculates the activation of the pressure control valve arrangement acting on the associated brake cylinder. The brake pressure is then adjusted to an optimum slip by the pressure control valve arrangement, which lowers, holds or builds up said pressure in accordance with the wheel behavior and hence with the friction conditions between the tire(s) and the road.
ABS pressure control valve arrangements without a relay action, to which the exemplary embodiments and/or exemplary methods of the present invention relate, are used on vehicles such as commercial vehicles, buses, semitrailer trucks and trailers. Pressure control valve arrangements without a relay action generally have 3/2-way solenoid valves as pilot control valves for diaphragm valves, wherein an electronic control device activates the 3/2-way solenoid valves to enable the functions required for ABS operation, “pressure holding”, “pressure reduction” and “pressure buildup”, to be carried out. During a braking operation which does not involve a response by the ABS (no tendency for a wheel to lock), the pressure medium, generally air, flows through the pressure control valve arrangements unhindered in both directions during air admission to and venting from the brake cylinders. This ensures that the operation of the service brake system is not affected by the ABS pressure control valve arrangement.
Within the housing, pressure control valves of the type in question in the form of single-channel pressure control valves for antilock systems of motor vehicles have respective diaphragm valves as a holding valve and an outlet valve and respective solenoid control valves for the holding valve and the outlet valve. The two diaphragm valves each contain a diaphragm, which can be acted upon by the pressure in a control chamber, wherein the control chamber is closed off from the outside by a cover secured on the housing.
A pressure control valve arrangement of the type in question for an ABS brake system is discussed in EP 0 266 555 A1, for example. In the prior-art pressure control valve arrangements, the housing has a pressure medium connection for pressure application and/or pressure relief, which is connected to a foot brake valve. Moreover, the two diaphragm valves are arranged on the side of the housing, wherein the corresponding pilot control spaces are closed off by covers secured on the side of the housing. These covers are produced by primary shaping processes such as injection molding, wherein passages or transverse channels are already allowed for during injection molding but transverse channels open on one side have to be covered by additional plastic closure parts. A cover shown in FIG. 2 of this document, for example, does admittedly have a transverse channel which interconnects a blind hole open toward the control chamber and a blind hole opening into a pressure medium channel in the housing and which is partially produced in the course of the injection molding process. However, owing to the molding process, this transverse channel is open at the outside of the housing and has to be closed off by a separate closure part. However, the production of this closure part and its mounting on the cover is associated with additional costs, accounting in total for a relatively high contribution to costs, given the large number of pressure control valve arrangements supplied by a supplier for vehicles.
If such a transverse channel 300 in the cover 270 is not formed partially in a primary shaping process but is produced by machining, there is the problem that the penetration of a drill from a radially outer boundary surface of the cover 270 then gives rise to an unwanted opening at this boundary surface in the transverse channel 300 extending between the blind holes 290a, 290b, and this opening must be re-closed by a ball 400 inserted into the opening, for example, as is evident from FIG. 6, which represents this prior art. In this method too, therefore, additional costs arise from the production and fitting of the ball 400.
Given this situation, it is the underlying object of the exemplary embodiments and/or exemplary methods of the present invention to provide a pressure control valve arrangement of the type mentioned at the outset in such a way that it is simpler and less expensive to produce and assemble. Moreover, the intention is to indicate a corresponding production method.
According to the exemplary embodiments and/or exemplary methods of the present invention, this object is achieved by the features described herein.